This invention relates to a catadioptric lens system having two reflecting surfaces, and, more particularly, to improvements of such system.
The catadioptric lens system has advantages over the dioptric lens system in that chromatic aberrations tend to be produced in a smaller degree, and that the physical length of the system can be remarkably shortened in the longitudinal direction. The general construction of the catadioptric lens system of the type described involves a front refracting lens, a primary mirror, a secondary mirror, and a rear refracting lens. This rear lens is required to achieve good correction of aberrations and the shortening of the physical length. For the support of this lens, in many cases, the primary mirror is utilized with the provision of a central hole bored therein. In machining the mirror to produce the hole, however, it is difficult to effect a sufficiently high dimensional control, while economically maintaining a production run of bored mirrors. To overcome this drawback, the primary mirror may be constructed with advantage to provide a lens in the central region thereof to which the rear refracting lens is to be cemented, as, for example, disclosed in Japanese Patent Application Publication No. Sho 47-1909.